The captcha image is not changed/refreshed after using the browser back button

Steps To Reproduce

1) goto signup page
2) enter user name, enter no e-mail address
3) enter the displayed captcha code
4) get APPLICATION ERROR 0001200 invalid e-mail address
5) use back button of the browser
6) see previous page with same captcha image
7) enter valid e-mail
8) get APPLICATION ERROR #1904 Confirmation hash does not match
9) use back button of the browser
10) still see previous page with same captcha image
11) click audio output
12) enter the code you heard (which is another than the one you see)
13) get success message

Activities

I found that the issue is reproducible with Safari 7.0 (9537.71) but not FF 24.0
Maybe this is a bug in Safari, some kind of too much optimizing of the image cache.
We shouldn't waste our time at the moment as this is a quite new browser version without any patches since first release.